A desirable photodetector is a two-color infrared detector having simultaneous sensitivity in two spectral bands. An array of same may be employed in a number of imaging applications wherein it is required to simultaneously detect radiation within two spectral bands that emanates from a scene within a field of view of the array.
In commonly assigned U.S. Pat. No. 4,885,619, Dec. 5, 1989, entitled "HGCDTE MIS Device Having a CDTE Heterojunction" K. Kosai discloses a metal-insulated-semiconductor device comprised of Group II-VI material.
In U.S. Pat. No. 4,847,489, Jul. 11, 1989, entitled "Light Sensitive Superlattice Detector Arrangement with Spectral Sensitivity" Dietrich discloses a detector arrangement comprising a plurality of photosensitive detector elements each of which has a multilayer structure of alternating positively and negatively doped photosensitive semiconductor material having a superlattice structure. A control voltage is said to control spectral light sensitivity and an optical filter arrangement is provided for dividing the photodetectors into an upper and lower effective spectral range group.
In U.S. Pat. No. 4,753,684, Jun. 28, 1988, "Photovoltaic Heterojunction Structures" Ondris et al. describe a three layer, double heterojunction Group II-VI photovoltaic structure that employs a minority current mirror.
In Japanese Patent No. 55-101832, Aug. 4, 1980, Makoto Itou discloses, in the Abstract, an infrared detector comprised of n-type HgCdTe having electrodes 2 and 3 arranged on opposite surfaces. A polarity of a biased voltage is switchably coupled to the electrodes 2 and 3. This device is said to enable rays of wide wavelength ranges to be detected by only one semiconductor detector.
An article entitled "Some Properties of Photovoltaic Cd.sub.x Hg.sub.l-x Te Detectors for Infrared Radiation", by J. M. Pawlikowski and P. Becla, Infrared Physics, Vol. 15 (1975) pp. 331-337 describes photovoltaic p-n junction detectors constructed of HgCdTe crystals and epitaxial films.
Its authors report that the position of a photosensitivity maximum is shifted within a spectral region of 1-9 microns by changing a molar fraction of cadmium.
In commonly assigned U.S. patent application Ser. No. 07/452,891, filed Dec. 19, 1989, entitled "Two Terminal Multi-Band Infrared Radiation Detector" Eric F. Schulte discloses embodiments of two-color radiation detectors. A bias source is switchably coupled to the detector for enabling first one and then another spectral band to be detected.
It is an object of this invention to provide a method of fabricating a two-color infrared radiation detector array that provides for an efficient use of detector surface area while obtaining enhanced device electrical and optical characteristics.
It is a further object of the invention to provide an array comprised of a plurality of three-layer n-p-n or p-n-p photodetector structures in which a middle, electrically common layer is electrically and physically continuous across the array, and wherein the top and bottom layers are each comprised of an alloy semiconductor having constituents selected for providing the top and bottom layers with a sensitivity to different spectral bands.
It is a still further object of the invention to provide a radiation detector array that enables simultaneous detection of radiation within two spectral bands.